1. Field of the Disclosure
This disclosure generally relates to the field of tractor-trailer vehicles and, in particular, safety devices for tractor-trailer vehicles.
2. Description of the Art
Tractor-trailer vehicles are typically formed of a tractor unit and a semi-trailer (hereinafter “tractor-trailer”) that are coupled together using an articulated connection. A common mechanism for coupling the tractor unit to the semi-trailer is a fifth wheel hitch or assembly (hereinafter “the fifth wheel”) on the tractor that is configured to receive a king pin on the semi-trailer. The king pin extends downward from the underside of the semi-trailer and is locked into position by the fifth wheel. (See U.S. Pat. Pub. 2011/0147142).
A fifth wheel may include a socket configured to receive and guide the king pin and a mechanical locking mechanism, including one or more mechanical jaws, that will restrict movement of the king pin when the fifth wheel is in the locked position. Unlocking of the locking mechanism will allow the king pin to be extracted and the tractor and semi-trailer (or “trailer”) to be separated or uncoupled.
When coupled, the tractor unit may supply electrical and pneumatic power to the semi-trailer. The electrical and pneumatic power may be delivered over cables and hoses or lines, respectively, which connect from the rear portion of the tractor unit to the front portion of the semi-trailer.
Typically, semi-trailer brakes are supplied with pneumatic power through two air lines running from the tractor unit to the semi-trailer. A main air supply line pressurizes the semi-trailer's air tank, and two air lines from the semi-trailers air tank provide air pressure to two sets of brakes—service brakes and parking brakes. A service air line is configured to supply pressurized fluid to the service brakes of the semi-trailer. The service brakes are activated when the pressurized fluid in the service air line is communicated to the service brakes on the semi-trailer, and the service brakes provide braking power under control of the driver, usually when the semi-trailer is in motion. A parking brake air line is configured to supply pressurized fluid to the parking brakes. The parking brakes prevent movement of the semi-trailer independent of the service brakes, usually when the semi-trailer is stationary. Air pressure in the parking brake air line releases the semi-trailer parking brakes, which are normally urged to the “on” position by springs when air pressure is absent. When the semi-trailer's air tank is pressurized, the fluid in an air line to the parking brakes is pressurized and the pressurized fluid is communicated to overcome the parking brake springs, which releases the parking brakes. The parking brake air line is also known as “the emergency air line” and “the red air line”.
Conventional Coupling
In order to couple a semi-trailer to a tractor unit, the tractor unit is reversed partially underneath the semi-trailer until the king pin, guided by the fifth wheel socket, is locked in position by the fifth wheel moveable jaws that automatically clamp around the king pin.
After reversing a tractor unit to a semi-trailer and locking the king pin with the fifth wheel, the driver may confirm that the king pin has been properly locked with the fifth wheel with the jaws of the fifth wheel. This confirmation can be performed using a test, commonly known as either a pull or snatch test, which typically involves shifting or selecting first gear in the tractor unit transmission and attempting to drive forward, thereby pulling against the semi-trailer with its parking brakes engaged by spring pressure. The pull test is commonly accepted as demonstrating that a proper coupling of the king pin with the fifth wheel has occurred if the tractor unit cannot move relative to the braked semi-trailer.
Split Coupling
Some combinations of a tractor unit and a semi-trailer are operated with a very small gap between the front of the semi-trailer and the rear of the tractor unit cab. This situation usually occurs when the operator or driver uses a long semi-trailer and is trying to keep the overall vehicle length within a certain limit. The small gap precludes the normal connection of air lines and electrical cables between the tractor unit and semi-trailer. Once the semi-trailer has been coupled to the tractor unit the size of the gap is insufficient for the driver to gain access between the front of the semi-trailer and the rear of the tractor unit. This situation generally requires a method of coupling a semi-trailer to a tractor unit commonly known as split coupling. Split coupling is an inherently dangerous procedure which involves connecting the air lines and electrical cables between a tractor unit and semi-trailer before the king pin of the semi-trailer is locked with the fifth wheel of the tractor unit.
Split coupling generally involves reversing the tractor unit close to, or partially under, the front of a semi-trailer but before the king pin locks with the fifth wheel socket. The driver then leaves the cab and manually operates one or more pneumatic valves fitted to the tractor unit, which blocks pneumatic fluid pressure to the air line that releases the semi-trailer parking brakes. The driver then connects the pneumatic lines and electrical cables between the tractor unit and the semi-trailer in the normal manner. Once the pneumatic lines and electrical cables are connected, the driver re-enters the cab and reverses the tractor unit until the king pin locks with the fifth wheel. Split coupling is clearly more complicated than the above discussed conventional coupling.
During split coupling, the manual valves that the driver needs to operate on different tractor units may not be standardized and confusion on the part of the driver may result in a dangerous situation where the semi-trailer parking brakes are released when the semi-trailer is not properly coupled to the tractor unit.
Over-Coupling
During the process of reversing a tractor unit under a semi-trailer to couple the semi-trailer to the tractor unit, it is possible for the king pin to entirely miss the guiding socket of the fifth wheel. This can occur due to the height of the tractor unit fifth wheel being low relative to the parked semi-trailer, in which case the king pin passes over the top of the fifth wheel, or by a sideways misalignment, causing the king pin to ride over the top surface of the fifth wheel on either side of the socket. When such an over-coupling error occurs, it is possible for the semi-trailer to be resting upon the fifth wheel with the king pin blocked in front of the fifth wheel. When this situation occurs the semi-trailer is commonly referred to as being over-coupled.
Performing a pull test with an over-coupled semi-trailer can give the impression that the semi-trailer is properly coupled as the tractor unit will not be able to move forward due to the blocked semi-trailer king pin in front of the fifth wheel. While performing a test in reverse gear would reveal the coupling error, this additional test is not always performed.
Generally, when performing conventional coupling, the driver leaves the cab of the tractor unit and connects the air lines and electrical cables to the semi-trailer after performing a pull test. The driver normally has to climb onto the tractor unit chassis between the rear of the cab and the front of the semi-trailer to make these connections of the air lines and electrical cables.
If a semi-trailer is over-coupled when the parking brake air line is connected and delivering pressure to the parking brakes, then the semi-trailer, with its parking brakes released, will be free to move relative to the tractor unit as the semi-trailer. This may result in the driver being injured between the front of the semi-trailer and rear of the cab if the semi-trailer rolls forward (e.g. due to parking on an inclined surface) or may result in the semi-trailer becoming detached from the tractor unit as the tractor unit is driven away.
The connection of the brake air lines involve a pair of tractor unit/trailer couplers (e.g. “glad hands”) with a flexible seal that allow pressure to equalize between the tractor unit/trailer couplers when connected and a self-seal to prevent loss of pressure from the main air tank when disconnected. Some tractor units use only a tractor unit/trailer coupler self-seal to prevent air pressure loss when not connected. Once the glad hands connection is made, a manual valve in the glad hands is opened which allows pressurized fluid to move between the tractor unit and the semi-trailer brake air lines. Thus, the semi-trailer parking brakes are released as soon as the glad hands connection for the brake air lines is made.
Tractor units are also equipped with parking brakes. It is not uncommon for drivers to forget to apply the tractor unit parking brake after performing a pull test. The driver may have the impression during the pull test is that the tractor unit parking brake is already applied because the semi-trailer parking brakes have not been released and the fifth wheel coupling between the tractor unit and semi-trailer prevents movement.
When the tractor unit parking brake air line is connected to the semi-trailer air line and air pressure is delivered to the parking brakes, the semi-trailer parking brakes are released and only the tractor unit parking brakes prevent the semi-trailer from moving. If the tractor unit parking brakes are not applied at this stage, then the tractor unit and semi-trailer vehicle will be free to move. It is not uncommon for drivers to be injured when such an unexpected vehicle movement occurs and this situation also presents third party risks.
In US Pat. Pub. No. 2011/0147142, a system is proposed which provides a warning indicator in the cab of a tractor unit when the handle of a fifth wheel is not in the locked position. The system is configured to alert the driver of the unlocked position of the handle and to prevent the application of the semi-trailer's service brakes while the tractor-trailer vehicle is in motion, thus preventing the separation of the semi-trailer from the tractor unit while the tractor-trailer vehicle is in motion.
In U.S. Pat. No. 6,100,794, a system is proposed which provides a warning indicator in the cab of a tractor when a king pin detector switch indicates the presence of a king pin in the proper location with a fifth wheel. The detector includes a second switch that turns off the warning indicator when the pull handle of the fifth wheel is moved to the locked position.
A shortcoming of the systems described above is that none of the prior art proposes a “no go” system to prevent movement of the tractor-trailer vehicle when the fifth wheel is unlocked before the tractor-trailer vehicle moves. Another shortcoming of the systems described above is that none of them detects the position of the fifth wheel locking mechanism. While U.S. Pat. Pub. No 2011/0147142 proposes a system configured to detect the king pin and the pull handle and U.S. Pat. No. 6,100,794 proposes a system configured to detect the presence of the king pin and the pull handle, neither is detecting the locked/unlocked position of fifth wheel itself. Another shortcoming of the systems described above is that a person may have to be between the tractor unit and the semi-trailer to release the semi-trailer parking brakes manually. Therefore, a need exists for a fifth wheel airlock safety system that prevents movement of the semi-trailer until a fifth wheel locked condition is detected. There is also a need for a fifth wheel airlock safety system that detects the fifth wheel locked condition based on the locked/unlocked position of the fifth wheel. Further, there is a need for a fifth wheel airlock safety system that automatically and remotely engages/disengages the semi-trailer parking brakes, which eliminates the release of the semi-trailer parking brakes based solely on the making of the glad hands connection for the air brake air lines by the driver and improves safety by reducing accidents due to drivers forgetting to set the tractor unit parking brake. There is also a need for a fifth wheel airlock safety system that allows the semi-trailer parking brake to be released based on the status of the fifth wheel coupling while the driver is in the tractor unit cab.